Method and apparatus to determine an initial flow rate in a conduit

ABSTRACT

A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of allowed parent Application Ser.No. 09/419,849, filed Oct. 19, 1999, to issue as U.S. Pat. No. 6,868,739on Mar. 22, 2005, entitled Method and Apparatus to Measure Blood Flow byan Introduced Volume Change, which parent application is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flow measurements, and moreparticularly to blood flow measurements in biomedical diagnostic andresearch applications, wherein a flow rate is determined from sensedrelative changes in the flow resulting from a known introduced volumechange in the flow.

2. Description of Related Art

Commonly used methods to measure blood flow in biomedical diagnostic andresearch applications include indicator dilution, transit-timeultrasound, Doppler ultrasound, electromagnetic, nuclear magneticresonance and x-ray fluoroscopy principles.

The measurement of blood flow is particularly important during vascularreconstructive procedures. In such procedures, the interventionalcardiologist/radiologist attempts to restore blood flow in a diseasedvessel, so measurement of the efficacy of the procedure constitutesimportant feedback. While prior methods have practical uses duringspecific medical studies and protocols, no method has been developedthat has found widespread use during vascular reconstructive procedures.

A well-accepted blood flow measurement technique employing indwellingcatheters is the indicator dilution method, often named Stewart-Hamiltonmethods after the inventors who pioneered this family of methods in thelate 19th and early 20th century. In this method, an additional elementis introduced into or extracted from the blood stream, or a bloodproperty is changed (the “indicator”). A calibrated sensor placeddownstream from the point of indicator introduction measures theabsolute concentration of the indicator. Via well known equations onecan then derive the volume flow at the point of mixing of the indicatorwith the blood flow. These methods are widely used for cardiac outputmeasurement using pulmonary artery catheters. The method has not founduse during interventional procedures likely because it requirespre-calibrated concentration sensors. The calibration of commonly usedsensors such as thermal or electrical is affected by changes in vesseldiameter.

Therefore, the need exists for determining flow rate in real time duringvascular interventional procedures where catheters may be introducedinto the patient. The need also exists for determining flow rate duringa medical procedure so that the efficacy of the procedure can bedetermined, thereby reducing complications and subsequent interventions.The need also exists for determining flow in a broad spectrum ofapplications, without requiring extensive modifications of surgicalprocedure or retraining of surgical staff.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a new class of flow measurement where aninitial flow, the flow to be measured, is purposely altered. Withoutlimiting the scope of this method, we will refer to this method herebyas the “volume change method”.

The present family of volume change methods to measure an initial flowrate implement the following steps: introducing (i.e., injecting orwithdrawing) a known volume of fluid over a known time (or measuredtime), that is, introducing a known flow rate to the initial flow ratesuch that the “introduced volume change” will produce one or more“resulting changes” in the flow to be measured; monitoring, directly orindirectly, values which correspond to the resulting changes; anddetermining the initial flow rate from the induced volume change and themonitored values.

The present invention further provides for the determination of flowsduring the introduced volume change. The invention also provides forcalibration of flow sensors and sensor methods. The volume change methodof measuring flow has a further usage as a means to calibrate the volumeflow sensitivity of flow sensors, pressure sensors and dilution sensors.The present invention may also employ blood velocity measurement,pressure measurement and indicator dilution measurement techniques.

The present invention also includes an apparatus for determining theflow rate in a conduit. The apparatus includes a sensor for sensing achange resulting from the introduction of a known flow rate and acontroller for determining the initial flow rate in the conduitcorresponding to the sensed change and the introduced known flow rate.

In a further application of the invention, a catheter is introduced intothe cardiovascular circuit of a patient, and specifically into thevessel in which the flow rate is to be determined. A metered volumechange is made to the initial flow in the vessel through the catheter.Resulting changes in the vessel flow (or corresponding values) aremonitored and the initial flow rate in the vessel is determined. Theresulting changes may be monitored by sensors located inside theconduit, outside the vessel, on the skin or even remote from thepatient.

The volume change method employs, in some of its embodiments, changes inindicator concentration as a means to assess relative changes in localflow in a conduit. These methods bear some similarity to theconventional indicator dilution family of methods, often calledStewart-Hamilton and Fick principle methods. Indicator dilution methodsuse indicator concentration as the primary means to assess blood flow,according to a simple principle: if one introduces a known amount ofindicator in a flow and monitors downstream the resulting absoluteconcentration of that indicator, one can deduce the volume rate of flow.Indicators are used differently in the volume change method. Inconventional indicator dilution methods the volume of the introducedindicator must be known and the concentration curve is recorded andanalyzed in adequate absolute units, such as “rems per ml/min” for aradioisotope indicator, or “calorie change per ml/min” for thermaldilution. No such absolute calibration is needed for the present volumechange method: in the indicator embodiments of the volume change method,only values proportional to concentration changes are required tocalculate the flow in the conduit. Neither the amount of the introducedindicator nor the actual concentration changes need to be determined.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic showing flows in a conduit with a side branch forintroducing a volume change.

FIG. 2 is a schematic showing flows for two spaced apart injectionsfunctioning as volume changes.

FIG. 3 is a representative view of a conduit having a catheter forintroducing a volume change and monitoring a resulting upstream changeand a resulting downstream change.

FIG. 4 a shows the recorded flow velocity upstream of an introducedvolume change.

FIG. 4 b shows the recorded flow velocity downstream of an introducedvolume change.

FIG. 5 shows a conduit and site of a volume injection with upstream anddownstream sensors located on the conduit, or the skin of a patient andremotely located.

FIG. 6 is a representative view of a conduit and adjacent sensorsselected to sense an upstream position and a downstream positionrespectively.

FIG. 7 is a representative view of a conduit and a single sensor sensingan upstream position and a downstream position.

FIG. 8 is a representative view of a catheter in a conduit, the catheterhaving a single sensor intermediate a pair of volume change sites.

FIG. 9 is a graph showing the relationship of sensed blood velocity totime at a single sensor for a first and a second introduced volumechange.

FIG. 10 is a representative view of a conduit showing a sensor outsidethe conduit in locations at the conduit wall, at the skin of the patientand remotely located.

FIG. 11 is a representative view of a conduit showing an indicatordilution catheter with two separate dilution sensors for a constantinfusion in combination with a single volume change.

FIG. 12 a is a graph showing the relationship of sensed indicatorconcentration to time at an upstream sensor after the introduced volumechange.

FIG. 12 b is a graph showing the relationship of sensed indicatorconcentration to time at a downstream sensor after the introduced volumechange.

FIG. 13 is a representative view of a conduit showing a catheter havingan indicator dilution sensor for use with a constant infusion combinedwith two separate injections.

FIG. 14 is a graph showing the relationship of sensed indicatorconcentration to time at a dilution sensor for a first and a secondintroduced volume change.

FIG. 15 is a representative view of a catheter in a conduit, thecatheter having two pressure sensors and one intermediate volume changesite.

FIG. 16 is a hydrodynamic schematic of a cardiovascular system duringblood flow measurement by induced volume change using a single volumechange and two pressure sensors.

FIG. 17 a shows the recorded pressures upstream of an induced volumechange.

FIG. 17 b shows the recorded pressures downstream of an induced volumechange.

FIG. 18 is a representative view of a catheter in a conduit, thecatheter having a single pressure sensor intermediate a pair of volumechange sites.

FIG. 19 represents the hydrodynamic schematic diagram of thecardiovascular system during blood flow measurement by introduced volumechange using two volume changes and a single pressure sensor.

FIG. 20 is graph showing the relationship of sensed pressure for a firstand a second induced volume change.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for the determination of a volumetricflow rate (“flow rate”) in a conduit by the volume change method. Theconduit may be any of a variety of liquid conducting members includingarteries, veins, heart chambers, shunts, vessels, tubes and lumens.Thus, the term conduit encompasses each of these as well as any otherflow-conducting element. The volumetric flow rate is a measure of thevolume of liquid passing a cross-sectional area of the conduit per unittime, and may be expressed in units such as milliliters per min (ml/min)or liters per minute (l/min). A liquid flow having a flow rate also hasa flow velocity, the distance traveled in a given time, such asmillimeters per second (mm/s). Thus, for liquid flowing in a conduit,there will be a flow rate (volumetric flow rate) having a flow velocity.

The present invention includes the volume change measurement methodwhich encompasses the following steps: (i) introducing a known volumechange to the flow to be measured; (ii) monitoring the relativechange(s) (or values corresponding to these) in the flow to be measuredwhich result from the introduced volume change; and (iii) calculatingthe initial flow in the conduit (i.e., the flow existing in the conduitbefore the introduced volume change) from the known volume change andthe relative change(s).

A volume change may consist of a circulating volume change or it may bea discrete volume change such as an injection or withdrawal of a volumeof liquid. The circulating volume change includes the simultaneouswithdrawal of liquid (such as blood) from the conduit and the returndelivery of the liquid (or a different liquid) back into the conduit,usually with a pump or other extracorporeal system. The returned liquidmay have been modified via a secondary system such as a blood treatmentdevice. The withdrawal and return delivery may be performed in differentvessels of the cardiovascular circuit. In contrast, the discrete volumechanges do not include simultaneous withdrawal and return of a liquid.That is, if there is a withdrawal or injection of liquid, the fluid flowduring this volume change is either into or out of the system, without acorresponding simultaneous flow in the opposite direction. A withdrawaland a subsequent injection to the initial flow is encompassed by thediscrete volume change as there is no circulating (simultaneouswithdrawing and injecting).

It is understood that the term “volume change” includes, but is notlimited to any and all methods that induce a change in the volumetricflow rate in the conduit in which flow is to be measured, including butnot limited to: the introduction of a known bolus of liquid into theliquid stream in the conduit; the withdrawal of a known bolus from theflow in the conduit; the simultaneous or successive introduction and/orwithdrawal of a plurality of boluses; the introduction or the withdrawalof a metered flow rate; the simultaneous or successive introductionand/or withdrawal of several metered flow rates; the combination of ametered flow rate change and a bolus injection or withdrawal; thestep-wise alteration of the diameter of a section of a catheter (orother variable cross section device) inserted into the flow stream inthe conduit, the introduction or withdrawal of a solid volume into/outof the flow stream in the conduit, and the alteration of the crosssectional volume of the conduit over a certain conduit length byaltering its cross sectional geometry. All of these introduce a meteredchange (known flow rate) to the flow to be measured in the conduit. Thismetered change in flow, independent of how the change is induced,constitutes the “volume change.” The volume change is a known volumeover a known time. That is, a known, (measured or measurable) change isintroduced to the initial flow whose flow rate is to be determined.

In the general case, the introduced volume change will effect changes tothe flow in the conduit both upstream and downstream from the site ofthe introduced volume change. However, it is understood, the changesresulting from the volume change may include changes to thecharacteristics, properties or parameters of the liquid (“liquidcharacteristic”) as well as the characteristics, properties orparameters of the flow (“flow characteristic”). This includes changesthat are proportional or correspond to the liquid or the flow. Forexample, if the liquid characteristics are sensed, the optical,electrical, thermal or material aspects may be sensed. Specifically, theelectrical conductivity, optical transmissivity, or temperature,velocity of sound or Doppler frequency. The flow characteristics includevelocity, rate or pressure of the flow.

To calculate the initial flow, one would therefore monitor changes inflow in the conduit, both upstream and downstream from the point of theinduced volume change in the flow. This can be implemented in twoconfigurations: one introduced volume change and two sensors, or twointroduced volume changes and one sensor.

In the first configuration, one sensor monitors changes to the conduitflow downstream of the introduced volume change, the other sensormonitors changes upstream of the introduced volume change. In the secondconfiguration one could alter the location where the volume change isintroduced: one volume change is induced upstream, the other volumechange is induced downstream of a sensor located at a fixed position. Inan alternative embodiment of the second configuration, the properties ofa single sensor could be changed such that one sensing location would beupstream, the other sensing location would be downstream from the fixedlocation where the volume change is introduced.

At certain positions within a flow geometry, the volume change will only(or predominately) affect the conduit flow downstream or upstream fromthe point where the volume change is introduced. For example, a volumechange introduced in a conduit connected to a fixed-output pump willonly affect flow downstream from the point of change. A changeintroduced at the base of the pulmonary artery will primarily changepulmonary flow and not the output of the right ventricle. In such cases,the volume change method can be implemented by only measuring relativechanges in flow downstream from the point of introduced volume change.

In other instances, the induced volume change will primarily alterconduit flow upstream from the point where the volume change isintroduced. For example, the microvasculature of a capillary networkrepresents a relatively large resistance to blood flow, while a healthyarterial bed feeding these capillaries may represent a relatively lowresistance to blood flow. At such a location, most of the introducedvolume change would flow retrograde in the introduced artery, and itwill suffice to measure relative changes in flow only upstream from thepoint of change introduction. The venous return path within thecardiovascular geometry, similarly, offers areas where a measurementsimplification can be made. The full venous return system operates at alow liquid pressure. Its capacity to accept an introduced liquidinjection is therefore great: the veins will just extend a bit to acceptthe introduced volume. However, the peripheral veins also incorporateone-way valves: retrograde flow is automatically blocked. Therefore, ifa volume change of sufficient magnitude is introduced in such a vein,the upstream flow will automatically drop to zero. This removes the needto implement an upstream sensor, and flow in the vessel can becalculated from just a downstream recording of the change of flow, thevolume change (the volume/unit time), and the flow configurationassumptions.

It is understood that the sensing of changes resulting from a volumeintroduction includes, but is not limited to any and all methods mayregister such a change: the direct measurement such a change, theindirect recording of a secondary affect caused by such a change, or therecording of an effect which corresponds to such a secondary affect.Without limiting the scope of the disclosed invention, the preferredembodiments focus on three such change sensing methods: sensing ofchanges in blood transport (flow or flow velocity), sensing changedblood chemical or physical properties (indicator dilution) and sensingchanges in pressure.

The volume change method of measuring flow has a further usage as ameans to calibrate the volume flow sensitivity of flow sensors, pressuresensors and dilution sensors. After the steps of introducing a change inflow and sensing the relative changes in flow which result from thevolume change, the calculation of the actual volume rate of flow in theconduit is synonymous to calculating the sensor's volume flowsensitivity. Thus, the velocity-to-volume flow conversion factor of aflow velocity sensor (such as an extracorporeal Doppler sensor,perivascular or intravascular transit time sensor or an implantedelectromagnetic sensor) and uncalibrated indicator concentration sensorcan be readily determined by the volume change method. The sensor can beemployed from then on (so long as its flow sensing geometry isunaltered) to report volume flow directly without the added steps of thevolume change method.

Theory

Referring to FIG. 1, a flow in a conduit 10 has an input (upstream) flowQu and outgoing (downstream) flow Qd. The conduit 10 can be an artery,vein, artificial vessel or any other channel of flow. Via a side branch12, a temporary flow Qi (the volume change) can enter or leave the flowconduit 10. In a typical clinical application as disclosed in thisinvention, as shown in FIG. 3, a catheter 20 is located in the conduit10. The catheter 20 includes a port 21 for introducing the volumechange, the port being intermediate an upstream sensor 30 and adownstream sensor 40. In a typical clinical application, Qi may resultfrom the volume change passing through the catheter port 21 between thepoints where Qu and Qd are monitored (FIG. 3). Assuming a steady-statecondition, where the volume of the conduit 10 does not change during themeasurement interval, the law of conservation of mass is applied todefine the relationships between these flows.

Before and after the volume change (injection/withdrawal) period, flowinto the conduit Qu equals flow out of the conduit Qd and equals initialflow Q:Q=Qu=Qd  (Eq. 1)

During the injection period (suffix i) the following flow equationdescribes the conservation of mass (see FIG. 1):Qui+Qi=Qdi  (Eq. 2)

Subtracting Eq. (1) from Eq. (2) and dividing the resulting equation byQ (=Qu=Qd) yields:

$\begin{matrix}{{\frac{{Qui} - {Qu}}{Qu} + \frac{Qi}{Q}} = \frac{{Qdi} - {Qd}}{Qd}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

Setting Qui−Qu=ΔQu and Qdi−Qd=ΔQd. ΔQu and ΔQd can be positive ornegative: a positive value indicates an increase in flow; a negativevalue indicates a decrease in flow. Rearranging the terms yields anexpression for the initial flow in the conduit:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\;{Qd}}{Qd} - \frac{\Delta\;{Qu}}{Qu}} \right)}} & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$

This equation is central to the present volume change method. It statesthat the undisturbed flow in the conduit 10 (vessel) before/after theintroduced volume change is calculated from the introduced volume change(here expressed by its flow rate Qi), and the relative measurement ofchanges in flow upstream and downstream from the volume changeintroduction site. For simplicity, the equation can be rewritten as:

$\begin{matrix}{Q = \frac{Qi}{\left( {{Cd} - {Cu}} \right)}} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$where: Cd=ΔQd/Qd, is the relative change in a flow-correspondingparameter downstream from the point where flow is changed, Cu=ΔQu/Qu, isthe relative change in a flow-corresponding parameter upstream from thepoint where flow is changed. In a typical implementation of the volumechange method where a bolus of liquid is injected, the downstream flowincreases (positive Cd) and the upstream flow decreases (negative Cu).So, the (Cd−Cu) factor is the sum of two positive numbers.

The ratio between Cd and Cu reveals where the resistance to changes inflow exists. If the volume change site (location) is just downstreamfrom a fixed-output flow source such as the heart, Cu will be near zero,and the flow Qh in such a vessel can be measured with a single sensor:

$\begin{matrix}{{Qh} = \frac{Qi}{Cd}} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

In other instances the downstream flow may be much more resistant tochange that the upstream flow, meaning that Cd can be neglected incomparison to Cu. Such may be the case at a volume change location nearthe capillary part of the cardiovascular circulation. In that instancethe flow Qc can be measured with a single sensor as:

$\begin{matrix}{{Qc} = \frac{Qi}{Cu}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

A third opportunity for a single sensor measurement exists in the venousvasculature at locations where one-way valves stop or inhibit retrogradeflow. If the introduced volume change consists of an injected flow whichis larger than the flow before the injection, flow upstream from theinjected volume change will drop to zero (Qui=0) during the volumechange period. Applying the definitions used above, Cu=−1, and the flowvalue Qv that existed in the vein before the volume change wasintroduced equals:

$\begin{matrix}{{Qv} = \frac{Qi}{\left( {{Cd} + 1} \right)}} & \left( {{Eq}.\mspace{14mu} 8} \right)\end{matrix}$

Returning to the general case described by Eq. 5, where a singleintroduced volume change is sensed by both an upstream sensor 30 and adownstream sensor 40, each sensor provides an output which correspondsto flow (FIG. 1), which provides a basis for further calculations.Before the volume change, the upstream sensor 30 reports measurementvalues Mu, the downstream sensor 40 reports a measurement values Md.Index i indicates the measurement values reported by these sensorsduring the introduced change:Mu=αQ  (Eq. 9)Md=βQ  (Eq. 10)Mui=αQui  (Eq. 11)Mdi=βQdi  (Eq. 12)

In these equations, α and β are the volume flow calibration factors forthe upstream sensor and the downstream sensor, respectively. CombiningEq. 5 with Eqs. 9 through 12 yields values for these volume flowcalibration factors:

$\begin{matrix}{\alpha = {\frac{Mu}{Qi}\left( {{Cd} - {Cu}} \right)}} & \left( {{Eq}.\mspace{14mu} 13} \right) \\{\beta = {\frac{Md}{Qi}\left( {{Cd} - {Cu}} \right)}} & \left( {{Eq}.\mspace{14mu} 14} \right)\end{matrix}$

Thus, the volume change method can be used to establish the volume flowcalibration factors of the upstream sensor 30 and the downstream sensor40.

By substituting these Eqs. 13 and 14 into Eqs. 11 and 12, the values forthe flows at the sensor locations during the introduced volume change inflow, Qui and Qdi can be calculated:

$\begin{matrix}{{Qui} = {\frac{{Mui} \cdot {Qi}}{Mu}/\left( {{Cd} - {Cu}} \right)}} & \left( {{{Eq}.\mspace{14mu} 15}a} \right) \\{{Qdi} = {\frac{{Mdi} \cdot {Qi}}{Md}/\left( {{Cd} - {Cu}} \right)}} & \left( {{{Eq}.\mspace{14mu} 15}b} \right)\end{matrix}$

FIG. 8 depicts a one-sensor 50, two volume change site (upstream site 51and downstream site 53) (injection/withdrawal ports) implementation ofthe volume change method. FIG. 8 depicts how this configuration may beimplemented in practice, using a double lumen catheter 22 with one flowparameter sensor 50. An index * is used for the flow definitions in thisconfiguration. Before the introduction of any volume change, thefollowing flows in all sections of the conduit 10 are equal to eachother:Q=Qu*=Qb*=Qd*  (Eq. 16)where Q*, Qu*, Qb* and Qd* are values of the initial blood flow, andblood flows upstream of, between, and downstream of the two volumealteration sites, respectively.

FIG. 8 depicts how this configuration may be implemented in practice,using a single catheter. The catheter 20 of FIG. 8 includes the upstreamport 51, a downstream port 53 and an intermediate sensor 50. Volumechanges can be introduced by first introducing an upstream volume changeinto the upstream port 51 in the catheter 22, then introducing adownstream volume change into the downstream port 53 of the catheter.For simplicity, the volume change in the upstream port 51 is selectedequal to the volume change into the downstream port 53 and =Qi. Flowmeasurements made during the injection will again be indicated by thesuffix i. There are now two different kinds of measurements on the Qbsensor 50: one where the sensor indicates the downstream flow changesresulting from the first injection (=Qbdi) and one where the sensorindicates upstream flow changes resulting from the second injection(Qbui). The conservation of mass principle yields the followingequations for the two injections:Qui*+Qi=Qbdi*  (Eq. 17a)Qbui*+Qi=Qdi*  (Eq. 17b)

We assume that the upstream flow change effected by the volume change atthe upstream port 51 is identical to the upstream flow change effectedby the volume change at the downstream port 53: Qui*=Qbui*. Similarly,we assume that the downstream flow change produced by the volume changeat the upstream port 51 is identical to the downstream flow changeproduced by the volume change at the downstream port 53: Qdi*=Qbdi*.These assumptions are closely approximated in cases where the flowresistance between the two sites of the introduced volume change isnegligibly small compared to the flow resistances upstream anddownstream of the volume change sites. Eqs. 17a and 17b can be rewrittenas a single equation with a sensor 50 in only the Qb position:Qbui*+Qi=Qbdi*  (Eq. 18)

This equation is in a form identical to Eq. 2, but this flow equation isnow realized by a two-volume change sites and a single sensor method.Following a derivation approach similar to the one followed for Eq. 2yields the volume change method equation for this one sensor 50intermediate two volume change sites 51, 53 configuration:

$\begin{matrix}{Q = \frac{Qi}{\left( {{Cbd} - {Cbu}} \right)}} & \left( {{Eq}.\mspace{14mu} 19} \right)\end{matrix}$

Cbd is the relative change in a flow-corresponding parameter from theupstream volume change introduction. Cbu is the relative change in aflow-corresponding parameter from the downstream volume changeintroduction.

This equation states that the initial flow in the conduit 10 (vessel) iscalculated from the introduced volume change (i.e. ml/min.), and therelative changes (or the values that correspond to these changes) inflow between the locations of the introduced volume change during thefirst upstream volume change and the second downstream volume change.

THE MEASUREMENT OF ONTRAVASCULAR BLOOD FLOW

Eight embodiments of a device for the measurement of blood flow in aconduit utilizing the present method and specifically an introduction ofknown volume change (volume/unit time) into an initial volume flow aredisclosed.

In a particular application of the invention, a catheter 20 is disposedin the flow to be measured. That is, the catheter 20 is located insidethe flow conduit to provide access for the introduced volume change. Thenecessary measurements of the resulting flow changes (indicator dilutionand/or flow velocity and/or pressure) can be made from sensors carriedon the catheter, located in the conduit, located on an exterior to theconduit, on the skin of the patient or even remotely located from thepatient.

In addition, the catheter 20 may serve the sole purpose of introducingthe volume change, or also accommodate the measurement of the resultingchanges in the initial flow, or also be combined with other catheterfunctions during surgical interventions such as, but not limited to flowrestorative procedures performed by the interventional radiologist andcardiologist including balloon angioplasty, thrombectomy, chemical andmechanical clot removal and stenting.

EMBODIMENT 1 (TWO SENSOR CATHETER TO MEASURE VELOCITY WITH SINGLEINJECTION)

As shown in FIG. 3, in the first embodiment, the catheter 20 with twosensors 30, 40 is employed to measure a velocity of blood (such as inm/sec) using a single volume change introduction through the port 21.The sensors 30, 40 may be any type of sensor as previously disclosed. Ina preferred construction, the sensors 30, 40 are connected to thecatheter 20 to be located within the conduit 10.

The catheter 20 is inserted into the conduit 10 as shown in FIG. 3. Thetwo sensors 30, 40 measure blood velocity, or a parameter thatcorresponds to flow velocity at their respective locations in theconduit 10. The first sensor 30 measures a parameter Vu, the secondsensor 40 measures a parameter Vd, each corresponding to flow velocityat its local respective site. Because flow velocity corresponds tovolume flow, an equation analogous to Eq. 5 is:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\;{Vd}}{Vd} - \frac{\Delta\;{Vu}}{Vu}} \right)}} & \left( {{Eq}.\mspace{14mu} 20} \right)\end{matrix}$where ΔVu and ΔVd are changes corresponding to upstream and downstreamblood flow velocities.

The results of Eq. 20 are independent of direct calculation of a valuefor cross sectional areas of the conduit 10 at the upstream sensor 30and the downstream sensor 40. An accurate measurement of Q using Eq. 20relies on the ability to measure baseline values corresponding to flowvelocity, Vu and Vd, as well as changes in the baseline ΔVu and ΔVd. Theintroduced volume change flow rate, Qi may be measured by using a knownintroduced volume, M, and dividing this known volume by the period ofinjection, T. Alternatively the introduced change may be implemented byusing an infusion/withdrawal pump set to volume change flow rate Qi.

The introduced volume M may be realized through the injection of a knownvolume of saline. FIG. 4 illustrates the characteristics of such aninjection made between two sensors 30, 40 wherein the sensors provide asignal corresponding to flow velocity. FIG. 4 a shows the recorded flow(blood) velocity for the sensor 30 upstream from the site of injection21, as shown in FIG. 3. FIG. 4 b shows the recorded flow (blood)velocity for the sensor 40 located downstream from the site of injection21. Baseline values Vu and Vd are shown for the upstream and downstreamlocations, respectively. The decrease in flow (blood) velocity recordedat the upstream sensor (ΔVu) produced from the injection of duration Tis shown in FIG. 4 a while the increase in flow (blood) velocityrecorded by the downstream sensor (ΔVd) over the same time period isshown in FIG. 4 b. These changes in flow (blood) velocity correspond toΔQu and ΔQd, the changes in the blood flow produced at the upstream anddownstream locations, respectively.

EMBODIMENT 2 (VELOCITY SENSORS OUTSIDE THE VESSEL WITH SINGLE INJECTION)

Referring to FIG. 5, in the second embodiment, flow (blood) velocitysensors 30, 40 are located outside the conduit 10 and a single volumechange introduction is made through port 21 in the catheter 20 which islocated in the conduit. This embodiment is analogous to Embodiment 1(Eq. 5 and Eq. 20) but sensors 30, 40 are located outside of the conduit10. Also shown in FIG. 5 are alternative locations for sensors 30′, 40′on the skin of the patient, or 30″,40″ spaced from the patient.

Referring to FIG. 6, the upstream sensor 30 and the downstream sensor 40may be adjacent each other and generally aligned along the relevant flowat the injection site 21, wherein each sensor defines a sensing zonesuch that an upstream sensor 30 sensing zone 33 extends upstream of theinjection site and a downstream sensor 40 sensing zone 43 extendsdownstream of the injection site. In a further configuration shown inFIG. 7, a single sensor 35 may selectively implemented to create anupstream sensing zone 33 and a downstream sensing zone 43.

EMBODIMENT 3: (SINGLE BLOOD VELOCITY SENSOR CATHETER WITH TWOINJECTIONS)

As shown in FIG. 8, the third embodiment employs the catheter 22 havinga single flow sensor 50, such as a blood velocity sensor, locatedintermediate two volume change site ports, an upstream port 51 and adownstream port 53, through which introductions are made into the flowin the conduit 10 through the catheter.

The catheter 22 is inserted into the conduit 10 (FIG. 8). In thisembodiment, flow may be measured by making two volume changeintroductions. One volume change is made upstream through the upstreamport 51, the other volume change is made downstream of the single sensor50 (blood velocity sensor) through the downstream port 53. The equationis analogous to Eq. 19.

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\;{Vd}}{V} - \frac{\Delta\;{Vu}}{V}} \right)}} & \left( {{Eq}.\mspace{14mu} 21} \right)\end{matrix}$

In this equation, V is blood velocity at the location of the singlesensor 50; ΔVd and ΔVu the changes in blood velocity from a volumechange introduction downstream of the sensor and upstream of the sensorrespectively. (FIG. 9).

The introduced volume change flow rate, Qi, may be determined bydividing a known injected or withdrawn volume of change, M by the timeperiod of the injection, T.

Intravascular flow can be measured with the single sensor system throughthe use of two isotonic saline injections. FIG. 9 shows thecharacteristics of such a method. A baseline blood velocity, V, ismeasured by the sensor. FIG. 9 shows the first injection. The firstinjection having been made downstream from the sensor, produces adecrease in V called ΔVu and occurs in a time period T1. The secondinjection, made upstream from the sensor, produces an increase in bloodvelocity at the location of the sensor, ΔVd, which occurs during timeperiod T2. Volume change injection flow rate, Qi, may be calculated bydividing injected or withdrawn volume M by T1 and T2.

EMBODIMENT 4: (SINGLE BLOOD VELOCITY SENSOR OUTSIDE THE CONDUIT WITH TWOINJECTIONS)

This approach is analogous to Embodiment 3 and Eq. 21. Referring to FIG.10, the catheter 20 is disposed into the vessel for providing access forthe introduced volume change. The catheter 20 includes an upstream port51 and a downstream port 53. The sensor 50 such as a blood velocitysensor is located outside the conduit. The location of the sensor 50 isnot limited to positioning in between the sites of induced volumechange, it is only important that the sensor measures velocity changesbetween the volume change sites. Also shown in FIG. 10 are alternativesites for sensor 50′ on the skin of a patient and 50″ spaced from thepatient.

NOTES ON EMBODIMENTS 1 THROUGH 4

The blood velocity (corresponding sensors) can derive their measurementfrom any part of the conduit, even near the walls, assuming the measuredparameters correspond to the average flow. Furthermore, only relativechanges enter into the calculation, so measured values need onlycorrespond to absolute velocity values. These aspects make themeasurement of intravascular flow with the present method relativelysimple, with accuracy and reproducibility based mainly on thesensitivity of the device for detecting relative changes correspondingto flow, and accurate determination of the introduced volume change, Qi.

The blood velocity-corresponding sensors may be located at any positionwhere a change may be sensed, such as: inside the conduit 20, on theconduit wall, further removed from the conduit within the patient'sbody, on the patient's skin, and outside the body. The location of thesesensors 50 is not limited to positioning before and after the volumechange introduction site. The sensors may be located close to each otherbut measure blood velocity upstream and downstream the volume changesite as shown in FIG. 6. It is contemplated that one sensor 35 as shownin FIG. 7 can be used, wherein the sensor periodically measures bloodvelocity upstream and downstream of the volume change site. For example,the upstream and downstream measurements can be performed by switchingthe direction of the generated ultrasound waves. The only requirement onsensor positioning is that one attains the proper upstream/downstreamgeometric relationship between each sensing site and volume changeintroduction site as described for Embodiments 1 through 4 and theiraccompanying figures.

It is also contemplated the sensors and the ports for volume changeintroduction may be located on different catheters. Volume changeintroduction may also be made from introducers and other accesses intothe conduit such as the sheaths and needles.

In each embodiment, the sensors may be of any type that has the abilityto measure relative (blood) flow, relative (blood) velocity or any valuecorresponding to the flow or the velocity. These sensors may be Doppler(ultrasound or optical), electromagnetic sensors, transit timeultrasound sensors, magnetic resonance sensor, sensors that measure thevelocity of blood by recording the injected media movement like X-ray,nuclear magnetic resonance sensors, or any other sensor producing asignal responsive to changes in flow.

EMBODIMENT 5: (INDICATOR DILUTION CATHETER WITH TWO SEPERATE DILUTIONSENSORS USING CONSTANT INFUSION Combined with Single Volume Change)

Referring to FIG. 11, this configuration employs an indicator dilutioncatheter 60 using constant infusion in conjunction with a single volumechange introduction. In one construction of this configuration, thecatheter 60 includes a constant infusion port 61 and a volume changeport 63 an upstream sensor 62 intermediate the constant infusion portand the volume change port, and a downstream sensor 64 downstream of thevolume change port. This embodiment describes intravascular flowmeasurement using a catheter 60 with a dilution sensor 62 which isinserted into the conduit 10. The constant infusion should have aduration sufficient to overlap the volume change period. To measure therelative changes of blood flow pursuant to Equation 5, a change inindicator concentration is monitored.

The upstream sensor 62 (a dilution sensor) is located upstream of thevolume change port 63 and the downstream sensor 64 is disposeddownstream of the volume change port 63. For purposes of description,the upstream sensor measurements are designated with a “u”, and thedownstream sensor measurements are designated with a “d” suffix.

The constant infusion serves to introduce an indicator upstream fromboth the sensors 62, 64. This indicator may be introduced anywherewithin the cardiovascular system, such as in a vein from where it passesthrough the heart into the artery where the volume change catheter 60 ispositioned. The following mathematical relationship exists for theinitial blood flow Q in the conduit 10 to be measured:

$\begin{matrix}{Q = {{Qu} = {{Qd} = {\frac{qku}{hu} = \frac{qkd}{hd}}}}} & \left( {{Eq}.\mspace{14mu} 22} \right)\end{matrix}$

In Equation 22, q is the rate of indicator infusion into conduit, ku andkd are calibration coefficients for the upstream sensor 62 and thedownstream sensor 64, respectively, hu and hd are the concentration ofthe indicator measured at the upstream sensor 62 and the downstreamsensor 64, respectively, as shown in FIG. 12.

An introduction of blood volume change between the sensors 62, 64produces a change in indicator concentration measured at the upstreamsensor 62 and a change in the conduit volume flow. The new flow equationis described mathematically in Equation 23a:

$\begin{matrix}{{Qui} = \frac{qku}{hui}} & \left( {{{Eq}.\mspace{14mu} 23}a} \right)\end{matrix}$

In Equation 23a, hui is the new level of the concentration recorded bythe upstream sensor 62 (see FIG. 12 a).

The same injection also produces a new level of flow and indicatorconcentration at the second (downstream) sensor 64:

$\begin{matrix}{{Qdi} = \frac{qkd}{hdi}} & \left( {{{Eq}.\mspace{14mu} 23}b} \right)\end{matrix}$

In Equation 23b, hdi is the new level of the concentration recorded bythe downstream sensor 64 (FIG. 12 b).

With a known introduced volume change flow rate, Qi, we substituteEquations 23a and 23b into the conservation of mass Eq. 2:

$\begin{matrix}{{Qi} = {q\left( {\frac{kd}{hdi} - \frac{ku}{hui}} \right)}} & \left( {{Eq}.\mspace{14mu} 24} \right)\end{matrix}$

Substituting Equation 22 into Equation 24 yields Equation 25:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{hd}{hdi} - \frac{hu}{hui}} \right)}} & \left( {{Eq}.\mspace{14mu} 25} \right)\end{matrix}$

Using indicator concentration change definitions: Δhu=hui−hu;Δhd=hdi−hd, this equation can be re-written in terms of relativeindicator concentration change:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\;{hu}}{hui} - \frac{\Delta\;{hd}}{hdi}} \right)}} & \left( {{Eq}.\mspace{14mu} 26} \right)\end{matrix}$

One finds from FIG. 12 that Δhd is negative; the denominator of Eq. 26is the sum of two positive numbers. Introduced volume change flow rate(Qi) can be calculated as a ratio of known volume change injection (M)divided by the time length of injection, T. The time period of theinjection may be recorded simply from the profile change of the dilutioncurves (see FIG. 12). As is the case for all volume change embodiments,one does not need to know the value of calibration coefficients ku andku of the indicator concentration sensors. All concentration levels inEq. 26 are expressed as ratios, meaning that only relative-sensingindicator devices are needed to implement the volume change method.

EMBODIMENT 6: INDICATOR DILUTION CATHETER USING CONSTANT INFUSIONCOMBINED WITH TWO SEPERATE INJECTIONS (FIG. 13)

Referring to FIG. 13, this embodiment describes intravascular flowmeasurement using a catheter 70 having a dilution sensor 72 which isinserted into the conduit 10. The catheter 70 includes an indicatorinfusion port 71, an upstream volume change introduction port 75 and adownstream volume change introduction port 73, wherein the sensor 72 isintermediate the upstream volume change introduction port and thedownstream volume change introduction port.

The first part of this method involves the creation of a continuouslyintroduced indicator upstream from the dilution sensor 72. This may beaccomplished through the upstream port 71. Initial flow in the conduit10 (vessel) Q to be measured is then described mathematically asfollows:

$\begin{matrix}{Q = {q\;\frac{k}{h}}} & \left( {{Eq}.\mspace{14mu} 27} \right)\end{matrix}$

In this equation q is the rate of indicator infusion, k is thecalibration coefficient related to the catheter sensitivity, and h isthe concentration level of the indicator during the infusion.

As a next step, a first Qi* volume change is introduced in the conduit10 (vessel) via port 73 in the catheter 70. The dilution sensor 72located upstream from the volume change site senses a new indicatorconcentration level hui (FIG. 14). The new upstream flow Qui isdescribed mathematically in Equation 28.

$\begin{matrix}{{Qui} = {q\;\frac{k}{hui}}} & \left( {{Eq}.\mspace{14mu} 28} \right)\end{matrix}$

A second volume change, Qi* is introduced via port 75. The dilutionsensor 72 located downstream from the volume change site at 75. Equation29 describes this mathematical relationship:

$\begin{matrix}{{Qdi} = {q\;\frac{k}{hdi}}} & \left( {{Eq}.\mspace{14mu} 29} \right)\end{matrix}$

In Equation 29, Qdi is flow at the dilution sensor location during theupstream volume change, hui is the new level of the concentrationrecorded by the sensor 72.

For simplicity, it is assumed that volume change injection flow, Qi*,was the same for both upstream and downstream volume changes. Thisassumption allows us to follow the derivation steps of Eqs. 24–26 toarrive at the following mathematical relationship:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\;{hu}}{hui} - \frac{\Delta\; h\mathbb{d}}{h{\mathbb{d}i}}} \right)}} & \left( {{Eq}.\mspace{14mu} 30} \right)\end{matrix}$

Thus, embodiment 5 and 6 are mathematically identical, and alldefinitions and comments made for Eq. 26 apply to Eq. 30 as well.

NOTES ON EMBODIMENTS 5 AND 6

The indicator introduction may be performed from the same catheter wheredilution sensor(s) are located or through another catheter or throughthe introducer, or through a needle. The indicator introduction furtherincludes but is not limited to adding substances to blood, withdrawingsubstances from blood or changing blood parameters (like heating orcooling) without adding or withdrawing substances from blood.

The indicator introduction may be performed anywhere within thecardiovascular system, for example, into a vein from where it passesthrough the heart into the artery where the volume change catheter ispositioned.

Usually the indicator infusion (or withdrawal) rate is much smaller thanthe initial blood flow rate and its influence on the initial blood flowin the conduit may me ignored. In the case of heating or cooling ofblood the indicator introduction causes no change in flow rate at all.In certain instances one may purposely choose an indicator introductionwhich doubles as a volume change introduction, and so arrange ameasurement sequence of steps or catheter configuration which isadvantageous for certain interventional procedures. For instance, thesecond volume change Qi* in the upstream site described in Eq. 29 may beimplemented with an injection solution which incorporates the indicatoragent as well, eliminating the need for the upstream continuousindicator infusion during this step of the procedural sequence. Thisapproach would eliminate the need for a separate upstream port for avolume change introduction.

In embodiments 5 and 6 the value of h is a concentration of indicator inblood. The embodiments may use common indicators but is not limited tothese: blood hematocrit, blood protein, sodium chloride, dyes, bloodurea nitrogen, glucose, lithium chloride and radioactive isotopes andmicrospheres. The blood concentration factors h appears in Eqs. 26 and30 only in the form of dimension-less ratios. This means that in theseembodiments no need exists for methods and devices which registerindicator concentration in absolute, calibrated units. Instead one mayemploy any method and device that produces relative, proportional orcorresponding indications of a selected blood concentration. One maythus select sensors which register values or its changes of any chemicalor physical parameters of blood that correspond to concentration. Theseembodiments may thus use, but are not limited to the following bloodproperties such as: blood electrical impedance, optical bloodproperties, blood temperature, blood density, blood pH, as well as bloodultrasound velocity. The sensors in each embodiment include any type ofsensors that record a corresponding measurement to such selected bloodproperties.

The indicator sensors may be located outside the conduit 10 (vessel),but preferably record the dilution curves in the vessel locationsupstream and downstream from the injection flow (embodiment 5) andbetween the injection flow locations for embodiment 6. These sensors maybe, but are not limited to, electrical impedance sensors, ultrasoundsensors and optical sensors.

It is further clear from Eq. 26 and 30 that the volume change approachdoes not require that the calibration coefficient k (see Eq. 22 and 27)be known. The results of the volume change measurement can be usedinstead to calibrate dilution sensors by calculating the value of k.Once the value of k is calculated, the same sensor can thereafter beemployed as a conventional indicator dilution sensor, with no need toperform separate volume change introductions.

EMBODIMENT 7 (TWO SENSOR CATHETER TO MEASURE PRESSURE WITH SINGLEINJECTION)

In a seventh embodiment shown in FIG. 15, a catheter 80 with two sensors82, 84 and an intermediate volume change injection port 81 is employedwhich measure blood pressure before and during a single volume changeintroduction. The sensors 82, 84 may be any type of pressure sensors.Further, the pressure sensors may be located inside or outside theconduit 10.

In a preferred construction, the sensors 82, 84 are connected to thecatheter 80 to be inserted into the conduit 10 as shown in FIG. 15. Thetwo sensors 82, 84 measure blood pressure or a parameter thatcorresponds to blood pressure at their respective locations in theconduit 10. The first sensor 82 measures an upstream value Pu and thesecond sensor 84 measures a downstream value Pd.

Referring to FIG. 16, the volume change equation for determining flow inthis embodiment can be derived from a hydrodynamic model of bloodcirculation in the vascular system. In FIG. 16, Ra and Rv represent thehydrodynamic resistances of the arterial and venous sides of thecardiovascular circuit leading to the upstream and downstream sensorsites, respectively. Ru and Rd are the hydrodynamic resistances of theflow conduit between the place of the volume change introduction and theupstream and the downstream sensor locations respectively.

The flow-pressure equations before the volume change introduction inEmbodiment 7 are as follows:Part−Pu=Q Ra  (Eq. 31)Pd−Pven=Q Rv  (Eq. 32)

During the volume change, conservation of mass at the volume changepoint is described by Eq. 2: Qui+Qi=Qdi. Therefore:Part−Pui=Qui Ra  (Eq. 33)Pdi−Pven=Qdi Rv  (Eq. 34)where Pui and Pdi are the new pressure levels in upstream and downstreamlocation respectively; Qui and Qdi are the new flows through thebranches upstream and downstream from the volume change introductionplace. Substituting Eqs. 33 and 34 into Eq. 2 yields:Qi=(Pdi−Pven)/Rv−(Part−Pui)/Ra  (Eq. 35)

In this equation, the variables Ra and Rv can be eliminated using Eqs.31 and 32:Qi=Q{(Pdi−Pven)/(Pd−Pven)−(Part−Pui)/(Part−Pu)}  (Eq. 36)

The pressures at the upstream and downstream sensing location areexpressed in terms of their change:ΔPu=Pui−Pu  (Eq. 37)ΔPd=Pdi−Pd  (Eq. 38)

Rearranging the terms then yields one of the expressions for flow Q asdetermined from the volume change Qi and pressure changes at theupstream and downstream sensing points:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\; P\mathbb{d}}{P{\mathbb{d}{- {Pven}}}} - \frac{\Delta\;{Pu}}{{Pu} - {Part}}} \right)}} & \left( {{Eq}.\mspace{14mu} 39} \right)\end{matrix}$

This is one of a number of ways to express the flow equation of thevolume change method when using pressure sensors. Pressure is a quantitywhich is always expressed relative to another site, as only pressuredifferences may produce flow. The Pd and Pu pressures may thus bereferenced to a number of points within the cardiovascular system, eachproducing a different form for Eq. 39. As an example, Pu and Pd may bereferenced to the point of the volume change introduction, Pi. In thisinstance the flow Q would be determined only from pressure differencesregistered on points along for instance a catheter containing the volumechange introduction port and three pressure sensors.

This type of intravascular flow measurement may be through injection ofa known volume (M) of isotonic saline. FIG. 17 a shows the recordedblood pressure for a sensor upstream from the site of injection. FIG. 17b shows the recorded blood pressure for a sensor located downstream fromthe site of injection. Baseline pressure values Pu and Pd are shown forthe upstream and downstream locations, respectively.

EMBODIMENT 8: (SINGLE BLOOD PRESSURE SENSOR CATHETER WITH TWOINJECTIONS)

As shown in FIG. 18, the eighth embodiment employs a catheter 90 havinga single flow (blood) pressure sensor 92, an upstream volume changeintroduction port 91 and a downstream volume change introduction port93, wherein two volume change introductions can be made into the flow inthe conduit 10 through the catheter 90.

The catheter 90 is inserted into the conduit 10 (FIG. 18). In thisembodiment, one volume introduction is made upstream of the sensor andone is made downstream of the single blood pressure sensor. The volumechange equation for this embodiment is derived in steps analogous to Eq.39:

$\begin{matrix}{Q = \frac{Qi}{\left( {\frac{\Delta\; P\mathbb{d}^{*}}{P{\mathbb{d}{- {Pven}}}} - \frac{\Delta\;{Pu}^{*}}{{Pu} - {Part}}} \right)}} & \left( {{Eq}.\mspace{14mu} 40} \right)\end{matrix}$where Pu and Pd are blood pressures measured at the sensor site(s)before each volume change introduction, ΔPu* and ΔPd* are the changes ofthe pressure due to volume change introduction upstream and downstreamof the sensor 92 respectively.

Intravascular flow can be measured with the single sensor system throughthe use of two isotonic saline injections. FIG. 20 shows thecharacteristics of such a method. FIG. 20 shows the first injection,made upstream from the sensor. This injection produces a pressureincrease in ΔPu* and occurs in a time period T1. The second injection,made downstream from the sensor, also produces also increase in bloodpressure ΔPd* at the location of the sensor, which occurs during timeperiod T2. Volume change injection flow, Qi, may be calculated bydividing injection or withdraw volume (M) by T1 and T2.

NOTES ON EMBODIMENTS 7 AND 8

Pressure measurements can be performed using any customary pressuresensing system located inside or outside the conduit. In a dual sensorsystem (7^(th) embodiment) one sensor may even be inside the conduit 10while the other is outside the conduit. Sensors as customarily used areliquid-filled catheters with a mechanical or electronic sensing devicepositioned at the end of the catheter outside the patient, electronicsensors positioned on the catheter inside the patient, but any othersensor system would suffice.

The volume change method may be implemented with further simplificationsin catheter configuration and sensor/injection port implementation. Asan example, embodiment 8 can be implemented using a double lumencatheter with each lumen channel alternately functioning as a volumechange port and liquid-filled pressure sensing channel. During a volumechange through the upstream port 91, pressures are sensed from thedownstream port 93 and vice versa. It is also understood the sensor 92may be omitted and the pressure monitored through the port which doesnot provide the respective volume change. As another example, one mayuse an extracorporeal pressure sensor positioned on the skin above anartery, and position a volume change introduction catheter inside thatartery to sequentially produce an upstream and a downstream volumechange introduction. Such sequential volume change introductions mayconsist, first, of the withdrawal of a volume of blood, then of there-injection of the same volume of blood.

EMBODIMENTS EMPLOYING COMBINATIONS OF BLOOD VELOCITY MEASUREMENT,DILUTION MEASUREMENT, AND BLOOD PRESSURE MEASUREMENT

It is clear from Eq. 4, 20, 26, and 39 that the upstream flow changesupon a volume change introduction are recorded independently of thedownstream flow changes upon a volume change introduction. This offersthe design freedom to mix and match all the sensing modalities disclosedin the previous embodiments (blood flow or velocity sensing, indicatorconcentration sensing, blood pressure sensing), with one modalityselected for the upstream, another modality for the downstream sensor.For example, relative flow change in the upstream location may bemeasured by a Doppler blood velocity sensor and simultaneouslydownstream changes may be recorded by a pressure sensor. Alternately, anupstream dilution sensor may be combined with a downstream pressuresensor, an intravascular pressure sensor may be combined with anextracorporeal flow velocity sensor, as examples. In such a fashion thedesigner of volume change instrumentation systems is given optimumdesign freedom to customize the measurement apparatus to suit a targetedthe surgical procedure.

NOTES ON ALL DISCUSSED EMBODIMENTS

The volume change method may be used anywhere within the cardiovascularsystem: in arteries, veins, in the heart, in arterio-venous shunts andother conduits within the body where flow can be altered via a volumechange introduction.

Besides providing intravascular flow measurements, an added benefit ofthe volume change method is the analysis of the relationship between theupstream and the downstream flow ratios (ΔVu/Vu vs. ΔVd/Vd in Equation20 and the analogous expressions in Eqs. 21, 26, 30, 39 and 40).Comparison of these ratios provides the user an indication of where themain resistance to the blood flow is located. In the case of vascularflow restorative procedures such as angioplasty, the main resistance toflow identifies the most hemodynamically significant stenosis, allowingthe operator to correct the most serious flow impediment when multiplestenoses are present. For example, when ΔVu/Vu is high when compared toΔVd/Vd, it means that there is a large resistance downstream from thesite of injection. When ΔVd/Vd and ΔVd/V are high, there is asignificant limitation to flow located upstream from the injection site.The ability to analyze this data allows the operator greater efficiencyin treating a stenosed vessel, reducing the need to correct a stenosisand then check flow in a trial and error attempt to identify the majorlimitation to flow.

For embodiments employing the sequential volume change in an upstreamand a downstream location, one may employ a single lumen catheter withupstream and downstream ports having one-way valves incorporated. Theone-way valves would be constructed such that a flow injectionautomatically opens one port, and a flow withdrawal automatically theother port. Alternately such a single lumen catheter may employalternate means to switch the volume change delivery between theupstream and the downstream port. Alternately one may use a singlelumen, single outlet catheter, and reposition the catheter outlet inrelation to the sensor (or vice versa) to achieve the desired upstreampositioning during one, and downstream positioning during the othervolume change.

As it is clear from the flow equations 4, 20, 21, 26, 30, 39 and 40,blood velocity, blood properties and blood pressure values are presentonly in the form of non-dimensional ratios. This means that all theseembodiments may instead employ uncalibrated sensors or sensors that onlyprovide values corresponding to the parameter referenced in the flowequations. Such corresponding sensors measurements may produce anymeasurement dimension such as “kilohertz” for an ultrasound Dopplersensor, or “bits” for an analog-to-digital converter output: thesedimensions are eliminated in the flow equation in the non-dimensionalsensor ratio expression.

The present invention contemplates a controller 100 for determining orcalculating the initial flow rate in the conduit 10 in response to thecorresponding signals from the respective sensor(s) and the introducedvolume change(s). The controller 100 may be any of a variety of devicesincluding a computer employing software for performing the calculations,or a dedicated analog circuit device, or a calculation routine intowhich measured parameters are manually entered. The controller 100 maybe connected to the sensor(s) and a flow rate monitor such as a pump forintroducing the volume change. It is understood the controller 100 coulddetermine the volume change from an input of the volume of the changeand the time over which the change was made.

While a preferred embodiment of the invention has been shown anddescribed with particularity, it will be appreciated that variouschanges and modifications may suggest themselves to one having ordinaryskill in the art upon being apprised of the present invention. It isintended to encompass all such changes and modifications as fall withinthe scope and spirit of the appended claims.

1. An apparatus for determining an initial flow rate in a conduit,comprising: (a) means for introducing a volume change to the initialflow rate; (b) an upstream sensor monitoring a change to the flowupstream of the introduced volume change; (c) a downstream sensormonitoring a change in the flow downstream of the introduced volumechange; and (d) a controller in communication with the upstream sensorand the downstream sensor for determining the initial flow rate.
 2. Theapparatus of claim 1, wherein the upstream sensor measures a first flowcharacteristic and the downstream sensor measures a different secondflow characteristic.
 3. The apparatus of claim 1, further comprising acatheter, the upstream sensor and the downstream being connected to thecatheter.
 4. The apparatus of claim 1, wherein the upstream sensorcreates an upstream sensing zone.
 5. The apparatus of claim 1, whereinthe downstream sensor creates a downstream sensing zone.
 6. Theapparatus of claim 1, wherein the controller determines the initial flowrate corresponding to the equation and analogous relationships,${Q = \frac{Qi}{{Cd} - {Cu}}},$ where Qi is the volume change flow rate,Cd is the relative change in a flow corresponding parameter downstreamfrom a location of flow change, Cu is the relative change in a flowcorresponding parameter upstream from the location of the flow change,and a Q is the initial flow rate.
 7. The apparatus of claim 1, whereinthe means for introducing a volume change to the initial flow rateincludes a catheter having an infusion port.
 8. A method of determiningan initial flow rate in a conduit, comprising: (a) introducing a volumechange at a location in the initial flow; (b) monitoring a resultingchange upstream of the location; (c) monitoring a resulting changedownstream of the location; and (d) determining the initial flow ratecorresponding to the monitored upstream change, the monitored downstreamchange and the introduced volume change.
 9. The method of claim 8,further comprising determining the initial flow rate corresponding tothe equation and analogous relationships,${Q = \frac{Qi}{{Cd} - {Cu}}},$ where Qi is the volume change flow rate,Cd Is the relative change in a flow corresponding parameter downstreamfrom a location of flow change, Cu is the relative change in a flowcorresponding parameter upstream from the location of the flow change,and a Q is the initial flow rate.
 10. An apparatus far determining aninitial flow rate in a conduit, comprising: (a) means for introducing avolume change to the conduit; (b) an upstream sensor upstream of theintroduced volume change, the upstream sensor measuring a changecorresponding to the introduced volume change; (c) a downstream sensordownstream of the introduced volume change, the downstream sensormeasuring a change corresponding to the introduced volume change; and(d) a controller in communication with the upstream sensor and thedownstream sensor, the controller configured to determine the initialflow rate in response to the measured changes.
 11. The apparatus ofclaim 10, wherein the controller determines the initial flow ratecorresponding to the equation and analogous relationships,${Q = \frac{Qi}{{Cd} - {Cu}}},$ where Qi is the volume change flow rate,Cd is the relative change in a flow corresponding parameter downstreamfrom a location of flow change, Cu is the relative change in a flowcorresponding parameter upstream from the location of the flow change,and a Q is the initial flow rate.
 12. The apparatus of claim 10, whereinthe means for introducing a volume change to the conduit includes acatheter having an infusion port.
 13. A method for determining aninitial flow rate in a conduit, comprising: (a) introducing a volumechange to the initial flow at a location intermediate an upstreampressure sensor and a downstream pressure sensor; and (b) determiningthe initial flow rate corresponding to a pressure sensed at the upstreampressure sensor and the downstream pressure sensor.
 14. An apparatus fordetermining an initial flow rate in a conduit, comprising: (a) a knownflow rate producer introducing a volume change to the initial flow rate;(b) a first sensor upstream of the introduced volume change, the firstsensor measuring an upstream change corresponding to the introducedvolume change; (c) a second sensor downstream of the introduced volumechange, the second sensor measuring a downstream change corresponding tothe introduced volume change; and (d) a controller in communication withthe first sensor and the second sensor, the controller configured todetermine the initial flow rate in response to the measured upstream anddownstream changes.
 15. The apparatus of claim 14, wherein the firstsensor measures one of a flow characteristic and a liquidcharacteristic.
 16. The apparatus of claim 14, wherein the first sensormeasures one of an optical property, electrical property, thermalproperty, acoustic property, pressure, sound velocity and Dopplerfrequency.
 17. The apparatus of claim 14, wherein the second sensormeasures one of a flow characteristic and a liquid characteristic. 18.The apparatus of claim 14, wherein the second sensor measures one of anoptical property, electrical property, thermal property, acousticproperty, pressure, sound velocity and Doppler frequency.
 19. Theapparatus of claim 14, wherein the controller determines the initialflow rate Q, corresponding to at least one of the following and ananalogous relationships:${Q = \frac{Q_{i}}{\left( {\frac{\Delta\; Q_{d}}{Q_{d}} - \frac{\Delta\; Q_{u}}{Q_{u}}} \right)}};\mspace{14mu}{Q = \frac{Q_{i}}{\left( {C_{bd} - C_{bu}} \right)}};\mspace{14mu}{Q = \frac{Q_{i}}{\left( {\frac{\Delta\; V_{d}}{V_{d}} - \frac{\Delta\; V_{u}}{V_{u}}} \right)}};$${Q = \frac{Q_{i}}{\left( {\frac{\Delta\;{hu}}{hui} - \frac{\Delta\;{hd}}{hdi}} \right)}};\mspace{14mu}{Q = \frac{Q\; i}{\left( {\frac{\Delta\;{Pd}}{{Pd} - {Pven}} - \frac{\Delta\;{Pu}}{{Pu} - {Part}}} \right)}}$where Q_(i) is the introduced volume during the introduced time;ΔQ_(d)=Q_(di)−Q_(d); ΔQ_(u)=Q_(ui)−Q_(u); Q_(d) is the flow ratedownstream of the introduced volume change Q_(l); Q_(u) is the flaw rateupstream of the introduced volume change Q_(l); C_(bd) is the relativechange in a flow corresponding parameter from an upstream introducedvolume change; C_(bu) is the relative change in a flow correspondingparameter from a downstream introduced volume change; ΔV_(u) is a changecorresponding to an upstream flow velocity; ΔV_(d) is a changecorresponding to a downstream flow velocity; V_(u) is an upstream flowvelocity; V_(d) is a downstream flow velocity; hu is a concentration ofindicator measured at an upstream sensor; hd is a concentration ofindicator measured at a downstream sensor; Δhu=hui−hu; and Δhd=hdi−hd.